4

LTC1756

PRES (Pin 1):(Input) Connects to the Smart Card acceptor’s

PRESENT indicator switch to detect if a card is inserted.

This pin has a pull-up current source so that a normally

open grounded switch can be detected with no external

components. The pull-up current source is nonlinear,

delivering higher current when the PRES pin is above 1V

but very little current below 1V. This helps resist false card

indications due to leakage current.

PWR (Pin 2): (Input) A low on the PWR pin places the

LTC1756 in the ACTIVE state enabling the charge pump.

The READY pin indicates when the card supply voltage

the Smart Card is possible. The reset and clock channels

are enabled after READY goes low. The I/O channel is also

enabled only after READY goes low.

The falling edge of PWR latches the state of the 5V/3V pin.

After PWR is low, changes on the 5V/3V pin are ignored.

GND (Pin 3): Ground Reference for the IC. This pin should

be connected to a low impedance ground plane. Bypass

the GND pin.

A 10

µF low ESR ceramic bypass capacitor is required on

this pin for optimum performance.

ing the actual output voltage with an internal reference

the LTC1756 switches to the Alarm state (see the State

capacitor to ground. For optimum performance a low ESR

ceramic capacitor should be used.

discharged to ground to comply with the deactivation

requirements of the EMV and ISO-7816 specifications.

I/O (Pin 6): (Input/Output) Smart Card Side Data I/O Pin.

This pin is used for bidirectional data transfer between the

microcontroller and the Smart Card. It should be connected

to the Smart Card I/O contact. The Smart Card I/O pin must

be able to sink up to 250

µA when driving the I/O pin low

due to the pull-up current source. The I/O pin becomes a

low impedance to ground during the Idle state. It does not

stable.

Once READY is low, the I/O pin is protected against short

The DATA-I/O channel is bidirectional for half-duplex

transmissions. Its idle state is H-H. Once an L is detected

on one side of the channel the direction of transmission is

established. Specifically, the side which received an L first

is now the input, and the opposite side is the output.

Transmission from the output side back to the input side

is inhibited, thereby preventing a latch condition. Once the

input side releases its L, both sides return to H, and the

channel is now ready for a new L to be transmitted in either

direction. If an L is forced externally on the output side, and

it persists until after the L on the input side is released, this

illegal input will not be transmitted to the input side

because the transmission direction will not have changed.

The direction of transmission can only be established from

the idle (H-H) state and is determined by the first receipt

of an L on either side.

RST (Pin 7): (Output) Level-Shifted Reset Output Pin. This

pin should be connected to the Smart Card RST contact.

The RST pin becomes a low impedance to ground during

the Idle state (see the State Diagram). The reset channel

does not become active until the READY signal goes low

Short-circuit protection is provided on the RST pin by

microseconds then the LTC1756 switches to the Alarm

has reached its final value (as indicated by the READY pin).

CLK (Pin 8): (Output) Level-Shifted Clock Output Pin. This

pin should be connected to the Smart Card CLK contact.

The CLK pin becomes a low impedance to ground during

the Idle state (see the State Diagram). The clock channel

does not become active until the READY signal goes low